1. Field of the Invention
This invention relates to electrochromic cells, and more particularly to accelerating the change in the electrochromic window from a high transmittance to lower transmittance state and making the change between transmittance states more uniform.
2A. Technical Considerations
Electrochromic devices have been proposed for use in alpha-numeric display panels in items such as digital watches, calculators and the like and in transparent windows. Electrochromic cells typically comprise a thin film of persistent electrochromic material, i.e. a material responsive to the application of an electric field or potential of a given polarity to change from a high transmittance, low-absorbing state to a lower transmittance, absorbing or reflecting state and remaining in the lower transmittance state after the electric field is discontinued, preferably until an electric field of reversed polarity is applied to return the material to the high transmittance state. The electrochromic film is in ion-conductive contact, preferably in direct physical contact, with a layer of ion-conductive material. The ion-conductive material may be solid, liquid or gel but is preferably a solid polymer layer. The electrochromic film and ion-conductive layers are disposed between two electrodes.
As voltage is applied across the two electrodes, ions are transported through the ion conducting layer. When the electrode directly adjacent to the electrochromic film is the cathode, application of a DC current causes darkening of the film, referred to as coloration. Reversing the polarity causes reversal of the electrochromic properties and the film reverts to its high transmittance state, referred to as bleaching.
2B. Patents of Interest
The following list of patents disclose various electrochromic transparency arrangements:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 3,521,941 Deb et al. 4,088,392 Meyers 4,088,395 Giglia 4,116,545 Reddy 4,174,152 Giglia et al. 4,335,938 Giglia et al. 4,361,385 Huang et al. 4,375,318 Giglia et al. 4,478,991 Huang et al. 4,645,308 Tracy et al. 4,768,865 Greenberg et al. ______________________________________
U.S. Pat. Nos. 4,294,867 and 4,388,522 to Boaz disclose heated transparencies with electroconductive ceramic heating elements.
U.S. Pat. No. 4,323,946 to Truax discloses an electrostatic charge reduction arrangement. Point source collectors extend through a dielectric material and are interconnected by an electrically conductive grid system that is connected to a ground.